Phosphorus halides

There are three series of binary phosphorus halides, containing phosphorus in the oxidation states +5, +3 and +2. All twelve compounds have been described, in varying degrees of detail, although serious doubts have been cast on the existence of PI5. (1)

Phosphorus pentafluoride is a relatively inert gas, notable as a mild Lewis acid and a fluoride ion acceptor. It is fluxional molecule. Phosphorus pentachloride and phosphorus pentabromide are ionic in the solid and liquid states, and are best described as PX4+PX6–. They are widely used as chlorinating and brominating agents in organic chemistry.

Phosphorus(II) halides may be prepared by passing an electric discharge through a mixture of the trihalide vapour and hydrogen gas. They are of purely academic interest at the present time. Diphosphorus tetrabromide is particularly poorly described.